1. Field of the Invention
This invention relates generally to a variable resistor. More particularly, the present invention relates to a chip-type variable resistor wherein the resistance can be adjusted by rotating a rotor relative to an insulating substrate which carries a printed resistor strip.
2. Description of the Prior Art
A variable resistor of the above-described type is disclosed for example in Japanese Utility Model Application Laid-open No. 2(1990)-17805. For conveniently describing the prior art, reference is now made to FIGS. 16 and 17 of the accompanying drawings.
As shown in FIGS. 16 and 17, the prior art chip-type variable resistor comprises an insulating substrate 1 made of a ceramic material for example. The substrate 1 has a central bore 1a, and carries a generally U-shaped resistor strip 2 including an arcuate portion which is centered about the central bore 1a. The respective ends of the resistor strip 2 are electrically connected to extremity electrode terminals 3, 4 arranged at one side of the substrate 1 as spaced from each other along said one side.
The underside of the substrate 1 carries an intermediate terminal member 6 which is made of a metal and integrally formed with a cylindrical support shaft portion 6a fitted in the central bore 1a of the substrate 1. A metallic rotor 5 is rotatably fitted on the shaft portion 6a of the terminal member 6 and has a downwardly directed contact portion 5a for coming into slidable contact with the resistor strip 2. Thus, the resistance of the variable resistor can be adjusted by turning the rotor 5 with a rotational range .theta.' (FIG. 2).
According to the prior art arrangement described above, the resistor strip 1 is uniformly formed to have a constant width and a constant thickness substantially over the entire length thereof. Thus, as shown in FIG. 18, if the nominal overall resistance R of the resistor is relatively large, the inclination (defined as dr'/d.theta.') of the resistance variation within the rotational range .theta.' of the rotor becomes inevitably steep. In such a case, it is possible to provide only a coarse adjustment of resistance.